Remove Included Propagators section from trace API spec (open-telemet…

…ry#1556)

* Remove Included Propagators section from trace API spec

This is a duplicate of the Propagators Distribution of the context
specification.

CHANGELOG.md

@@ -17,6 +17,7 @@ release.
 - Clarify the description for the `TraceIdRatioBased` sampler needs to include the sampler's sampling ratio. ([#1536](https://github.com/open-telemetry/opentelemetry-specification/pull/1536))
 - Define the fallback tracer name for invalid values.
   ([#1534](https://github.com/open-telemetry/opentelemetry-specification/pull/1534))
+- Remove the Included Propagators section from trace API specification that was a duplicate of the Propagators Distribution of the context specification. ([#1556](https://github.com/open-telemetry/opentelemetry-specification/pull/1556))
 
 ### Metrics
 

specification/trace/api.md

@@ -750,10 +750,6 @@ be called concurrently.
 
 ## Included Propagators
 
-The API layer or an extension package MUST include the following `Propagator`s:
-
-* A `TextMapPropagator` implementing the [W3C TraceContext Specification](https://www.w3.org/TR/trace-context/).
-
 See [Propagators Distribution](../context/api-propagators.md#propagators-distribution)
 for how propagators are to be distributed.